Today, medical technology imaging systems play an important role in the examination of patients. The representations of the internal organs and structures of the patient generated by the imaging systems are used to diagnose causes of disease, to plan operations, in the performance of operations, and to prepare therapeutic measures. Examples of such imaging systems are ultrasound systems, x-ray computer tomography (CT) systems, positron emission tomography (PET) systems, single-photon emission tomography (SPECT) systems, or magnetic resonance systems.
In a magnetic resonance system, the object under examination is exposed to the most uniform possible, static basic magnetic field (e.g., referred to as the B0 field). As a result, the macroscopic magnetization in the body is aligned parallel to the direction of the B0 field. Moreover, radio frequency pulses (also referred to as the B1 field) are radiated with radio frequency transmit antennas into the object under examination, their frequency being in the range of the resonant frequency, known as the Larmor frequency, of the nuclei to be excited (e.g., hydrogen nuclei) in the magnetic field. By these radio frequency pulses, the macroscopic magnetization in the object under examination is excited in such a way that the macroscopic magnetization is deflected through a “flip angle” from its equilibrium position parallel to the basic magnetic field B0. The macroscopic magnetization precesses initially around the z-direction and gradually relaxes once more. The magnetic resonance measurement signals (MR signals) generated in this relaxation of the nuclear magnetization are captured as so-called raw data by radio frequency receive antennas. The magnetic resonance images of the object under examination are reconstructed on the basis of the acquired raw data, where a spatial encoding is carried out using fast-switched gradient (e.g., magnetic) fields that are superposed on the basic magnetic field during the transmission of the magnetic resonance radio frequency pulses and/or the acquisition of the raw data.
Today, local coils are normally used as coils for receiving the MR signals of the object under examination. These local coils are MR antenna element arrays that include one or more MR antenna elements, e.g., in the form of conductor loops. These local loops are disposed during the examination relatively close to the body surface, as directly as possible on the organ or body part of the patient to be examined. In contrast to larger antennas more distant from the patient, the local coils offer the advantage that the local coils are disposed closer to the areas of interest. The noise components caused by the electrical losses in the antennas themselves and within the body of the patient are thereby reduced, as a result of which the signal-to-noise ratio of a local coil is in principle better than that of a more distant antenna.
The MR signals received by the MR antenna elements are normally also preamplified in the local coil and guided out of the central area of the magnetic resonance system via cables and fed to a shielded receiver of a MR signal processing device. The received data is then digitized in the latter and further processed for the imaging. An increasing number of MR antenna elements within a local coil or an increasing number of local coils during an examination consequently results in an increased requirement for cables for transmitting the MR signals. However, a multiplicity of cables slows down the attachment of the local coils to the object under examination, resulting in longer treatment times and therefore higher treatment costs. In addition, it is assumed that a multiplicity of the patients perceive a large number of cables as intrusive. Moreover, the investigation space within a MR system is limited, which limits the use of a multiplicity of cables, e.g., if the patient is moved on an associated bed facility. The aforementioned restrictions apply particularly if analog response signals are transmitted by the MR antenna elements, since shielded (e.g., coaxial) cables may have a large cross section and a high weight and are expensive.
In DE 101 48 462 C1, a device is described with which the MR signals of a plurality of MR antenna elements are transmitted wirelessly. However, the wireless transmission has the disadvantage that a high bandwidth is required with the data volume to be transmitted and a multiplicity of transmit channels that are intended to be operated in parallel. On the other hand, the available free bandwidth is small, since a multiplicity of electromagnetic signals already occurs in the range of MR systems. With increasing bandwidth, the measures required to avoid disturbances, in particular electrical interference, over a very wide frequency range incur considerable cost.